Motor driven fuel pump having impeller

ABSTRACT

A fuel pump for an internal combustion engine includes a suction-side cover having a fuel inlet, an exhaust-side cover having a fuel outlet, an electric motor, a pump casing disposed between the electric motor and the suction-side cover, an impeller disposed between the suction-side cover and the pump casing to be rotated by the electric motor, and a cylindrical housing for accommodating the suction-side cover, the pump casing and the impeller. The suction-side cover is made of a resinous member that has a shoulder having a round surface in contact with a portion of the cylindrical housing that is clinched at the shoulder.

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present application is based on and claims priority fromJapanese Patent Application 2003-90910, filed Mar. 28, 2003, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a motor driven fuel pump mountedin a fuel tank of an internal combustion engine (hereinafter referred toas engine).

[0004] 2. Description of the Related Art

[0005] A fuel pump that has a fuel pressurizing passage and an impellerto boost pressure of fuel is well known and disclosed, for example, inJP-B2-3052623. Such a fuel pump is comprised of a suction-side cover inwhich a portion of the fuel pressurizing passage is formed.

[0006] In order to reduce the production cost and weight, many trials tochange material of the suction-side cover from a metal to a resin hasbeen made. However, if a resinous suction-side cover 94 is fixed to acylindrical metal housing 92 by clinching the edge of the housing 92 asshown in FIG. 7, the resinous suction-side cover 94 easily deforms,resulting in that the suction-side cover 94 interferes with an impeller96. The resinous suction-side cover 94 may creep under continuouspressure from the housing in a long period of time, resulting inloosening of the suction-cover.

SUMMARY OF THE INVENTION

[0007] Therefore, an object of the invention is to provide aninexpensive and lightweight fuel pump that has a resinous suction-sidecover and is free from the above described problem.

[0008] According to a feature of the invention, a fuel pump for aninternal combustion engine includes a suction-side cover having a fuelinlet, an exhaust-side cover having a fuel outlet, an electric motor, apump casing disposed between the electric motor and the suction-sidecover, a passage member having a pressure boosting passage disposedbetween the suction-side cover and the pump casing, an impeller disposedin the pressure boosting passage to be rotated by the electric motor anda cylindrical housing for accommodating the suction-side cover, the pumpcasing and the impeller. In the above fuel pump, the suction-side coveris made of a resinous member that has a shoulder having a round surfacein contact with a portion of the cylindrical housing that is clinched atthe shoulder.

[0009] Therefore, the stress concentration on the suction-side coverbecomes smaller and creeping of the suction-side cover can be prevented.As a result, the suction-side cover can be prevented from loosening.

[0010] In the above described fuel pump, the round surface is preferablydisposed at a peripheral surface of the suction-side cover away from thepump casing. Further, the radius of the round corner is preferably 20 mmor longer. The portion of the cylindrical housing that is clinched mayhave a surface formed by a punch that has a concave pressing surface. Itis more preferable that the shoulder has a thickness between 4 mm and 5mm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other objects, features and char acteristics of the presentinvention as well as the functions of related parts of the presentinvention will become clear from a study of the following detaileddescription, the appended claims and the drawings. In the drawings:

[0012]FIG. 1 is an axial cross -sectional view of a fuel pump accordingto a preferred embodiment of the invention;

[0013]FIGS. 2A, 2B and 2C respectively illustrate a front view of asuction-side cover, a cross-sectional view of the suction-side cover cutalong line IIB-IIB in FIG. 2A, and a rear view of the suction-sidecover;

[0014]FIG. 3 illustrates a step of fixing the suction-side cover to ahousing of the fuel pump;

[0015]FIG. 4 is a graph showing a relationship between the amount ofdeformation of the suction-side cover and the radius of a pressingsurface of a punch for fixing the suction-side cover to the housing ofthe fuel pump;

[0016]FIG. 5 is a graph showing the amount of deformation of thesuction-side cover fixed by a punch having a curved surface;

[0017]FIG. 6 is a graph showing the amount of deformati on of thesuction-side cover fixed by a punch having a flat conical surface; and

[0018]FIG. 7 is a schematic diagram showing a conventional step offixing a suction-side cover to a cylindrical cover.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] A fuel pump according to a preferred embodiment of the inventionwill be described with reference to the appended drawings.

[0020] As shown in FIG. 1, a fuel pump 10 according to a preferredembodiment of the invention is a so-called in-tank type fuel pump to bemounted in a fuel tank of a vehicle.

[0021] The fuel pump 10 includes a cylindrical metal housing 22, whichhas a pair of annular steps 20, 30 at the inside surface thereof. Thehousing 22 accommodates an exhaust-side cover 14, an electric motor 46,a pump casing 40, an impeller 37, a suction-side cover 36, etc.

[0022] The exhaust-side cover 14, which has a front surface and ashoulder portion, is fitted to the housing 22 so that the front surfaceengages the annular step 20. The housing 22 has one end through whichthe exhaust-side cover 14 is inserted and fixed by clinching the edge ofthe one end to hold a shoulder portion of the exhaust-side cover 14,thereby positioning the exhaust-side cover 14 between the annular step20 and the one end. The electric motor 46 has a rotary shaft 45, whichis supported by the exhaust-side cover 14 via a bearing 16. The housing22 has an inner wall, on which four semi-cylindrical permanent magnets44 are disposed in a circular line. The permanent magnets 44 aremagnetized in radial directions to alternately form N and S poles in thecircumferential direction.

[0023] The electric motor 46 has an armature 42 which is rotatablyaccommodated in the housing 22 and a commutator 18 which is fixed to oneend of the armature 42. The armature 42 includes a magnetic core 24 towhich the rotary shaft 45 is force-fitted and a plurality of coils 28each of which is wound around a bobbin 26. The commutator 18 has aplurality of commutator segments each of which is connected to one ofthe coils 28.

[0024] The pump casing 40 is inserted into the other end of the housing22 and engages the annular step 30 by an inside surface thereof. Thepump casing 40 has an annular peripheral portion at an outside surfacethereof and a center hole to which another bearing 38 is fitted. Theannular peripheral portion engages the suction-side cover 36 at theinside surface of the suction-side cover 36. The suction-side cover 36has a shoulder 34 at the peripheral portion, which is held by a portionof the other end of the housing 22 that is clinched to fix thesuction-side cover 36 to the housing 22, thereby positioning the pumpcasing 40 between the annular step 30 and the suction-side cover 36. Apressure boosting passage 32 is formed at a space between the insidesurface of the suction- side cover 36 and the outside surface of thepump casing 40 so that the impeller 37 can rotate therein. The impeller37 is a disk member that has a plurality of blade-ditches on theperiphery thereof.

[0025] When the electric motor 46 rotates along with the rotary shaft 45to rotate the impeller 37, fuel that is supplied from the fuel inlet tothe pressure boosting passage 32 is pressurized and discharged from thepressure boosting passage 32 to the inside of the electric motor 46through a connecting passage 29. The discharged fuel cools the electricmotor 46 and flows out from the fuel outlet 12 to be supplied to anengine.

[0026] The suction-side cover 36 is a resinous disk plate that has aplurality of depressions 54 for preventing mold shrinkage and theshoulder 34 at its periphery. The suction-side cover 36 also has aC-shaped groove 50 that is a portion of the pressure boosting passage.The fuel inlet 52 is formed at an end of the C-shaped groove 50, and avapor purging hole 48 is also formed in the C-shaped groove 50.

[0027] The suction-side cover 36 has a thickness of t1, such as 7 mm.The shoulder 34 has a thickness of t2 and a round corner of more than 2mm in radius r2. The round corner provides a contact surface in contactwith the end of the housing 22. The more the radius of the round cornerincreases, the less stress concentration on the contact surface. As thestress concentration becomes smaller, creeping of the suction-side cover36 can be prevented or reduced. As a result, the suction-side cover 36can be prevented from loosening. However, as the suction-side cover 36becomes thicker, the total length of the fuel pump 10 increases.Therefore, the ratio of the thickness t2 of the shoulder 34 to thethickness t1 of the suction-side cover 34 is preferably between 0.57 and0.71.

[0028] The suction-side cover 36 is fixed to the housing 22 by a punch56, as shown in FIG. 3. The punch 56 has a pressing surface 58 to pressthe end of the housing 22 against the shoulder 34 of the suction-sidecover 36. The pressing surface 58 inclines to the center axis of thehousing 22 by an inclination angle α. As the inclination angle αincreases, the remaining stress to deform the suction-side cover 36becomes smaller. However, if the inclination angle α becomes larger than45 degrees, the housing 22 may buckle. Therefore, the inclination angleα is preferably about 30 degrees. The pressing surface is, preferably,concave that has a radius r1. It may be conical if the inclinationangleα is appropriate.

[0029] The amount of the deformation of the shoulder 34A relative to theradius r1 of the concave pressing surface 58 when the suction-side cover36 is fixed to the housing 22 at an end that has a thickness of 0.6 mmwas tested to have a result shown in FIG. 4. If the radius r2 of thecontact surface of the shoulder 34 is 1 mm, the amount of thedeformation of the shoulder 34 is smaller in case the radius r1 of thepressing surface 58 is 2 mm or 3 mm. If the radius r2 of the contactsurface of the shoulder 34 is 2 mm, the amount of the deformation of theshoulder 34 is smaller in case the radius r1 of the pressing surface 58is 4 mm or 5 mm.

[0030] According to the result of an analysis, the followingrelationship was found: if the radius r1 of the pressing surface 58 is alength between 1.4 mm and 2.4 mm larger than the sum of the radius r2 ofthe shoulder 34 and the thickness of the housing 22, the deformation dueto fixing by clinching becomes minimum; and if the radius r1 of theconcave pressing surface 58 is between 2 and 5, the deformation of theshoulder 34 becomes smaller than the flat conical pressing surface.

[0031] A result of an analysis of the deformation at two portions P, Q(shown in FIG. 2B) of the suction-side cover 36 is shown in FIGS. 5 and6. When the housing 22 and the shoulder 34 are fixed by clinching theend of the housing 22, the suction-side cover 36 deforms so that thesurface becomes convex in the direction away from the impeller 37.Therefore, the suction-side cover 36 will not interfere with theimpeller 37. The amount of the deformation when fixing by the punchhaving the concave pressing surface was found smaller than that whenfixing by the punch having the flat conical pressing surface.

[0032] In the foregoing description of the present invention, theinvention has been disclosed with reference to specific embodimentsthereof. It will, however, be evident that various modifications andchanges may be made to the specific embodiments of the present inventionwithout departing from the scope of the invention as set forth in theappended claims. Accordingly, the description of the present inventionis to be regarded in an illustrative, rather than a restrictive, sense.

What is claimed is:
 1. A fuel pump for supplying fuel to an internalcombustion engine comprising a suction-side cover having a fuel inlet,an exhaust-side cover having a fuel outlet, an electric motor disposedbetween said suction-side cover and said exhaust-side cover, a pumpcasing disposed between said electric motor and said suction-side cover,a passage member having a pressure boosting passage disposed betweensaid suction-side cover and said pump casing, an impeller disposed inthe pressure boosting passage to be rotated by said electric motor, anda cylindrical housing for accommodating said suction-side cover, saidpump casing and said impeller, wherein said suction-side cover comprisesa resinous member that has a shoulder having a round surface in contactwith a portion of said cylindrical housing that is clinched at saidshoulder.
 2. The fuel pump as claimed in claim 1, wherein said roundsurface is disposed at a peripheral surface of said suction-side coveraway from said pump casing.
 3. The fuel pump as claimed in claim 2,wherein the radius of said round corner is 2 mm or longer.
 4. The fuelpump as claimed in claim 2, wherein the portion of said cylindricalhousing that is clinched has a surface formed by a punch that has aconcave pressing surface.
 5. The fuel pump as claimed in claim 1,wherein said shoulder has a thickness between 4 mm and 5 mm.
 6. A fuelpump for supplying fuel to an internal combustion engine including asuction-side cover having a fuel inlet, a pump casing, an impellerdisposed between said suction-side cover and said pump casing and acylindrical housing for accommodating said suction-side cover, said pumpcasing and said impeller, wherein: said suction-side cover has ashoulder having a round surface in contact with a portion of saidcylindrical housing that is clinched at said shoulder; said roundsurface has a radius of 2 mm or longer; and said shoulder has athickness between 4 mm and 5 mm.